So, as periodically happens to me, what started as an idle curiosity turned into an experiment. I took a look at a RIB snapshot from Friday, from one of the RouteViews collectors, to see how common it is that a block gets advertised by two different ASes, as a whole block by one, and as a set of smaller blocks by the other. It turns out there's a non-trivial amount out there -- 490 blocks broken up, adding 1,815 prefixes announced, accounting for 19,623 RIB entries. More details below; let me know if you're interested in even more. Seems kind of interesting, as a form of deaggregation that doesn't show up in things like the CIDR report (since it's not within a single AS). (Standard caveats apply: This is a quick pass, not controlled for things like two ASes belonging to the same entity.) --Richard Total number of deaggregated prefixes: 490 Total additional prefixes advertised: 1815 Total additional RIB entries: 19623 (0.5% out of 3530845 total entries) Total addresses affected: 78863360 (roughly 1,203 /16s) Extremal points: 1. Largest deaggregated block: 17.0.0.0/8, advertised by AS7018 (AT&T), deaggregated into two /9s by AS714 (Apple Engineering) 2. Most fractured block: 58.140.0.0/14, advertised by AS3786 (LG DACOM, KR), deaggregated into 69 prefixes (ranging from /17 to /24) by AS10036 (C&M Communication, KR). Distribution of the number of additional prefixes: Prefixes Count 2 343 3 13 4 80 5 5 6 1 7 4 8 17 9 5 10 1 11 1 14 1 15 1 16 6 17 1 20 2 32 7 34 1 69 1 Distribution of prefix lengths deaggregated: Len Count 8 1 11 1 12 3 13 9 14 17 15 22 16 47 17 25 18 29 19 65 20 52 21 56 22 69 23 92 24 2 Distribution of the number of addresses affected: Addresses Count 512 2 1024 92 2048 69 4096 56 8192 52 16384 65 32768 29 65536 25 131072 47 262144 22 524288 17 1048576 9 2097152 3 4194304 1 33554432 1